1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to circuit breakers including a trip indicator. The invention also relates to trip indicators for circuit breakers.
2. Background Information
Circuit breakers are generally old and well known in the art. Circuit breakers are used to protect electrical circuitry from damage due to a trip condition, such as, for example, an overcurrent condition, an overload condition, an undervoltage condition, a relatively high level short circuit or fault condition, a ground fault condition or an arc fault condition.
Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the case, or automatically by way of a trip mechanism in response to the trip condition.
Typically, a circuit breaker operating mechanism includes a cradle assembly which is operable between a latched configuration during normal circuit breaker operation, and an unlatched position in which the separable contacts are tripped open, in response to the trip condition as detected by the trip mechanism. The circuit breaker has a number of operating handle positions corresponding to the status of the separable contacts. For example, a three-position circuit breaker has three operating handle positions, an ON position corresponding to the separable contacts being closed, a second position corresponding to the circuit breaker being OFF, and a third, intermediate tripped position wherein the separable contacts are tripped open in response to the trip condition. For two-position circuit breakers on the other hand, the OFF position is also the tripped position. Specifically, when the trip condition occurs and the two-position circuit breaker trips, the operating handle is automatically forced to the OFF position, and an automatic reset mechanism automatically resets the cradle assembly after the trip condition occurs, typically while the operating handle remains in the OFF position. Therefore, the breaker is automatically ready to be turned back ON by manually pivoting the operating handle to the ON position.
In view of the shared OFF and tripped positions of this latter type of circuit breaker, there is no way to quickly visually determine the status of the circuit breaker. It is nearly impossible to determine whether the circuit breaker has tripped or has been intentionally, manually turned OFF. This is problematic in that there is no opportunity to readily identify the occurrence of a trip condition or the source of the trip condition, in order that the problem may be rectified. The problem is even more pronounced when the circuit breaker is one of a plurality of circuit breakers arranged within the same panelboard, perhaps with several breakers already being intentionally turned OFF or, for example, where the handles of several of the circuit breakers are locked in the ON position using, for example, a padlock.
To help alleviate this problem, three-position circuit breakers have been known to include a trip indicator in the circuit breaker to indicate the tripped condition. Generally, the trip indicator comprises an indicator assembly which interacts with the operating handle or cradle of the circuit breaker in order to position a visual indicia, such as a trip flag, that may include printed words indicative of the circuit breaker status (e.g., “T”, “TRIPPED”, “ON” or “OFF”), beneath a lens or window which covers an opening in the circuit breaker housing. The flag or other indicia is actuated, in response to the trip condition, by the cradle. For example, when the cradle unlatches in response to the trip mechanism and pivots, the separable contacts of the circuit breaker are opened and the cradle forces the flag to the indicating position. Since the position of the flag is dependent upon the position of the cradle, the flag remains visible in the indicating position until the operating handle is manually reset, thereby relatching the cradle and drawing the flag away from the indicating position.
It will be appreciated that the foregoing indicator design is not conducive for use with two-position, automatically resetting circuit breakers. More specifically, because the trip flag is dependent upon the cradle, if such a design were employed in an automatically resetting circuit breaker, the trip flag would only momentarily be visible while the cradle was in its corresponding unlatched position. The flag would then immediately be drawn away from the indicating position by the cradle as it automatically reset (i.e., relatched). Moreover, such designs do not address instances in which a trip condition occurs but the operating handle has not yet moved to the OFF or tripped position, for example, where the circuit breaker has tripped but the operating handle is padlocked in the ON position, as previously discussed. Under such circumstances, known trip flags provide no indication of the trip condition, thereby making it nearly impossible to identify which circuit breaker among a group of breakers has tripped. Thus, for two-position automatic reset circuit breakers, the problem of not being able to identify whether or not a particular circuit breaker has tripped, remains.
There is a need, therefore, for a trip indicator capable of providing an indicia of the trip condition irrespective of the position of the operating handle or cradle of the circuit breaker.
There is, therefore, room for improvement in trip indicators for circuit breakers, such as automatic reset two-position circuit breakers, and in circuit breakers employing trip indicators.